This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Breast cancer is the most common malignancy in Western women. Tamoxifen is an agent commonly used to treat breast cancer which blocks some of estogen's actions on the breast and other tissues. In randomized trials, tamoxifen has established "proof of principle" for breast cancer chemoprevention by reducing breast cancer risk in women at increased risk of breast cancer. However, rare but life-threatening side effects of tamoxifen, including endometrial cancer, blood clots in lungs and legs and stroke have severely limited general use of tamoxifen for risk reduction. The current study will evaluate whether exemestane either alone or together with celecoxib can reduce the risk of breast cancer with a favorable risk to benefit ratio in otherwise healthy postmenopausal women at increased risk for developing breast cancer based on their age or mammogram breast density. For entry, women must be postmenopausal and be at increased breast cancer risk based on a calculated Gail risk score incorporating family and reproductive history, age 60 years or greater, a certain prior benign breast biopsy results. Women with concurrent NSAID use and those with recent menopausal hormone therapy or SERM use are not eligible. Participants will have a history and physical exam at baseline, blood tests and recent prior mammogram and bone density test (DEXA). A quality of life questionnaire and information on other medication will be collected.